Undead drinking blood?

Hello!

My world is heavily inspired by Darksouls, as such its main theme is battling the Curse of Undeath. The vast majority of undead in this world are mindless, lesser undead. They are relatively dangerous but can be dispatched by a skilled knight-hunter.

Very few less undead however manage to evolve into higher undead and regain their sentience. They also become immortal, with more durable bodies then humans. Both lesser and higher undead feed on human souls. These souls serve as both sustenance and a source of power.

Im trying to come up with the criteria for undead being able to devour someones souls. The only thing Im settled on is that the undead must deal a mortal blow in order to be able to eat a soul. This however makes undead sorcerers way too strong. So the next criteria could be that the undead must be in physical contact with the victim.

I was also wondering if instead of physical contact, the undead would have to drink some of the victims blood or maybe eat some of their flesh in order to get their soul. I have been told that drinking blood would have them labeled as vampires and I really dont want that. But I still think its a cool concept.

Do you guys think I should go with it? Does it make sense for an undead having to ingest blood before taking a soul?